This study will optimize catheter design for the cure of atrial fibrillation and ventricular tachycardia by radiofrequency (RF) ablation. In the USA about 2 million people are affected by some form of atrial fibrillation. Each year about 200,000 patients are treated for ventricular tachycardia. Atrial fibrillation, although itself not fatal, is a frequent cause of stroke and is linked to a high degree of cardiovascular mortality. Ventricular tachycardia is the main cause of sudden cardiac death, affecting particularly patients with myocardial infarction. Studies confirm the superiority of catheter ablation in the cure of monomorphic ventricular tachycardias. To cure atrial fibrillation, the physician would have to create, by RF ablation, long, thin lesions along trajectories similar to those postulated by the MAZE or Corridor procedures. For the cure of ventricular tachycardia, wide and deep lesions created by RF ablation were found therapeutically successful. This study will develop complex finite element (FE) models and perform experimental tests to optimize the design of ablation catheters capable of producing long thin lesions for the cure of atrial fibrillation (AFIB). It will also develop complex numerical models and perform experimental tests to optimize the design of ablation catheters capable of creating wide and deep lesions for the cure of ventricular tachycardia (VT). This research will include creation of maps of electrical and thermal properties of the organs lying in the thorax, for the range of voltages, current densities and temperatures applicable to RF ablation. These data will be used to create realistic and complex FE models for electrical- thermal FE analyses. Acquisition of a collection of CT scans of swine thoraxes will be used for developing correct geometry for FE models for the swine studies. Improvement of CT scans of human thoraxes, such as subsets for: (a) normal men; (b) normal women; (c) obese men; (d) obese women; (e) children, will be used to develop geometrically correct FE models for the human studies. These models will be used to research optimal ablation catheter design for the therapy of AFIB and VT. Experimental tests will validate temperature and electric field distributions predicted by the swine FE models. Simulations will find the optimal catheter design for the cure of AFIB and VT. These tests will determine: (a) optimal electrode/catheter geometry; (b) optimal placement of inner temperature sensors for the purpose of efficient temperature- controlled RF ablation; (c) optimal power application and ablation procedure duration. These findings will clarify the electrical-thermal response of the catheter-tissue system during RF ablation. Experimental tests on swine will verify the models. Recommendations for optimal ablation catheter design for human use having applications for the therapy of AFIB and VT will be disseminated.